[Mgs] Mgs Digest, Vol 132, Issue 2

Wed May 2 19:31:49 MDT 2018

Thanks, Paul. I needed that:). I left my plug gap alone.
Monte

On May 2, 2018 5:04 PM, <mgs-request at autox.team.net> wrote:

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Today's Topics:

   1. Re: spark plug gap (PaulHunt73)
   2. Re: spark plug gap (David F. Darby)

----------------------------------------------------------------------

Message: 1
Date: Wed, 2 May 2018 08:38:46 +0100
From: "PaulHunt73" <paulhunt73 at virginmedia.com>
To: <mgs at autox.team.net>
Subject: Re: [Mgs] spark plug gap
Message-ID: <2BAFF5F88B354081AD1F4A70167C3FF1 at paul>
Content-Type: text/plain; charset="iso-8859-1"

Ignition systems have for decades been more than capable of generating a
spark that will jump gaps much bigger than the plugs we use, up to 1/4" in
my tests with the system as used in the MGB and cars of that era.  However
that generates very high voltages which can break down ignition components
like cap, rotor, lead insulation and even the coil.  It's the size of the
plug gap plus that between rotor and cap contacts which determines the peak
voltage in the ignition system, and it's the requirement for that peak
voltage not to exceed a certain amount that leads to the manufacturer
specifications for plug gap.

When an ignition coil generates a spark it generates a certain amount of
energy which is dependant upon the design of the system, and modern
electronic ignition systems generate a lot more energy than ours.  If a
lead is removed from a plug with the engine running this will generate
voltages much higher than ours - so much so that they come with health
warnings, but the plug gap has typically only increased by a few
thousandths of an inch.

When an ignition system fires the voltages rises over time - a very short
time.  When it reaches the breakdown voltage of all the air-gaps in the
system i.e. plug and cap to rotor (where applicable) the plug fires and
current starts to flow.  At that point the voltage doesn't rise any
further, the energy starts to dissipate as current, and the higher the
energy produced by the system the longer the current will flow.  It's the
duration of the spark that is more relevant to modern high-energy systems
than the length of the spark i.e. plug gap.

PaulH.
  ----- Original Message -----

  I always thought that the larger gap gave a bigger spark and was better,
as long as the system generated a spark capable of jumping that far.  The
gap was a compromise, big enough, but not so big that you end up with no
spark.  Modern cars are more capable of reliably handling the larger gap.
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Message: 2
Date: Wed, 2 May 2018 08:40:24 -0500
From: "David F. Darby" <ddarby at centurytel.net>
To: mgs at autox.team.net
Subject: Re: [Mgs] spark plug gap
Message-ID: <2dde6447-690a-2bc5-cf2f-9013bf4f4333 at centurytel.net>
Content-Type: text/plain; charset="windows-1252"; Format="flowed"

Paul,

Thanks for that good explanation.

David

On 5/2/2018 2:38 AM, PaulHunt73 via Mgs wrote:
> Ignition systems have for decades been more than capable of generating
> a spark that will jump?gaps much bigger than the plugs we use, up
> to?1/4" in my tests with the system as used in the MGB and cars of
> that era.? However that generates very high voltages which can break
> down ignition components like cap, rotor, lead insulation and even the
> coil.? It's the size of the plug gap plus that between rotor and cap
> contacts which determines the peak voltage in the ignition system, and
> it's the requirement?for that?peak voltage not to exceed a certain
> amount?that leads to the manufacturer specifications for plug gap.
> When an ignition coil generates a spark it generates a certain amount
> of energy which is dependant upon the design of the system, and
> modern?electronic ignition systems generate a lot more energy than
> ours.??If a?lead is removed from a plug with the engine running this
> will generate voltages much higher than ours - so much so that they
> come with health warnings, but the plug gap has typically only
> increased by a few thousandths of an inch.
> When an ignition system fires the voltages rises over time - a very
> short time.? When it reaches the breakdown voltage of all the air-gaps
> in the system i.e. plug and cap to rotor (where applicable) the plug
> fires and current starts to flow.? At that point the voltage doesn't
> rise any further,?the?energy starts to dissipate as current, and the
> higher the energy produced by the system the longer the current will
> flow.? It's the?duration of the spark that is more?relevant to modern
> high-energy systems than the length of the spark i.e. plug gap.
> PaulH.
>
>     ----- Original Message -----
>
>     I always thought that the larger gap gave a bigger spark and was
>     better, as long as the system generated a spark capable of jumping
>     that far.? The gap was a compromise, big enough, but not so big
>     that you end up with no spark.? Modern cars are more capable of
>     reliably handling the larger gap.
>
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